Wan broadband access technology V EPON Technology

3.2.2、ONU Ranging and time delay compensation

When ONU After successful registration ,OLT According to the specified bandwidth allocation policy and each ONU Status report for , Dynamically give each ONU Allocate bandwidth ( Timeslot ). In a OLT port (PON port ) Exit interface , be-all ONU And OLT Of PON The clocks between ports are strictly synchronized , every last ONU Only by OLT The time allotted to it begins , Use the time slot length allocated to it to transmit data .

Make it clear in one sentence OLT As the standard time , Specify the time interval between sending data , It's different ONU Sending packets will not conflict .

every last ONU distance OLT Dissimilarity , There will be different delays . If there is no time delay compensation mechanism , That will produce various ONU Transmission conflict . therefore EPON Adopt ranging and delay compensation mechanism , Let the uplink data not interfere with each other .

Registration process , First step ONU send out GATE( Registration authorization ), This has a start time 、 The length of the time window 、 Timestamp field OLT Local clock information . With OLT The clock is the reference clock , Also on ONU Perform idle slot authorization (Grant). It can be understood in this way ：

ONU received OLT The data of is adjusted to the local clock OLT Reference clock . At this time, there is already a delay in the transmission process , At this time, adjust to OLT The reference clock of has time delay .

It's time to OLT Send after the length of the given time window REGISTER_REQ Registration request message .OLT After receiving the registration request information, compare your sending time , Calculate the round trip delay (RTT).

Introduce ranging and time delay compensation technology , Is to accurately measure each ONU To OLT Distance of , And precisely adjust ONU Transmission delay .

RTT(Round Trip Time, Round trip delay ), Refers to the uplink transmission delay + Downlink transmission delay ,RTT The unit is TQ(Time Quantum, Quantum of time ),1TQ=16ns, Referring to 1Gbps The rate of transmission 2B The time taken by the data .RTT and Distance(OLT To ONU Distance of , The unit is rice. ) The formula is ：
RTT=(Distance+157)/1.6393

General situation ,1km The length of the optical fiber can form about 630 Of RTT value .

RTT The calculation of ：
1、OLT issue GATE news , There is... In the news OLT Our local time T1.
2、ONU received GATE after , Adjust the local clock to OLT Reference clock T1, And authorize according to the time slot (Grant) The delay time of T2 Send it all the time REGISTER_REQ Registration request message ,
3、OLT received REGISTER_REQ The time to register the request message is T3.
4、OLT Calculate the downstream and upstream one-off RTT( Round trip delay )=T3-T2.

RTT compensate , stay OLT Delay compensation on the side , Send to ONU The authorization of reflects due to RTT Arrival time of compensation . for example , If OLT stay T Receive data at any time ,OLT The transmission includes the beginning of the time slot GATE＝T-RTT. The minimum delay defined between the timestamp and the start time , In fact, it allows processing time . The maximum delay defined between the timestamp and the start time , Keep the network synchronized .

By setting larger RTT, expand EPON Coverage of the system , Let as many as possible ONU Registered successfully .

3.2.3、 Ethernet OAM Workflow

OAM（Operation Administration and Maintenance, Operation and maintenance management ） It refers to the actual needs of network operation of operators , The management of the network is usually divided into 3 Categories: ： operation （Operation）、 management （Administration）、 maintain （Maintenance）, abbreviation OAM. Operation mainly completes the analysis of daily network and business 、 forecast 、 Planning and configuration ; Maintenance mainly refers to the daily operation activities of network and its business testing and fault management .

function ：OAM Find out 、 Link monitoring 、 Remote fault indication 、 Remote loopback test 、 Extensibility ;
Scope of monitoring and detection ： Packet loss 、 Time delay 、 shake 、 Link connectivity .

Ethernet OAM Working at the data link layer , Its protocol message is called OAMPDU（OAM Protocol Data Units,OAM Protocol data unit ）. Ethernet OAM It is through the regular interaction between devices OAMPDU To report link status , Enable the network administrator to effectively manage the network .

Ethernet OAM The process of establishing a connection is also called Discovery Stage , Is this end OAM Entity discovery remote OAM Entity 、 And establish a stable dialogue with it . When OAM After the entity receives the configuration parameters of the opposite end , Decide whether to establish OAM Connect . When both ends OAM Entity to Loopback function 、 After the check of configuration information such as unidirectional link detection and link events passes , Ethernet OAM The agreement began to work properly .

1、 standard OAM Found that the establishment is complete .
2、 Report supported OUI(Organizationally Unique Identifier, Globally unified logo ) And extend OAM Version number .
3、OLT confirm ONU Reported OUI And extend OAM Whether the version number is OLT In the supported list , There is , Build success ; non-existent , Establish a failure .

3.2.４、 Bandwidth allocation

Bandwidth allocation is divided into static and dynamic , The static bandwidth is determined by the size of the open window , Dynamic bandwidth is based on ONU The need for , from OLT Distribute .

DBA(Dynamic Bandwidth Allocation, Dynamic bandwidth allocation ) It is a polling based bandwidth allocation scheme . use DBA It can improve the utilization of uplink bandwidth , With the same bandwidth, it can carry more end users , So as to reduce user costs .ONU Report to in real time OLT Report on current business needs （Request）（ Such as ： All kinds of businesses are ONU Cache level ）,OLT Assign according to priority and time delay control requirements （Grant） to ONU One or more time slots , each ONU Send data frames according to the service priority algorithm in the allocated time slot . thus it can be seen , because OLT The object of allocating bandwidth is ONU All kinds of businesses rather than end users , about QoS Such an end-to-end service , There must be high-level agreement to ensure .

Uplink frame of dynamic slot allocation .MPCP Agreed Report Processing Report processing ,OLT according to ONU Of Report Application information , Realize the control of each ONU Dynamic bandwidth allocation and real-time status monitoring .

1、 from OLT Send a single in unicast GATE( Registration authorization ) Messages used to allocate transmission time slots .

2、ONU received GATE after ,Report Messages deliver local cache usage to OLT, To help OLT Intelligently allocate time slots .

4.EPON Basic equipment configuration

OLT Equipment is an important office equipment , It can be connected with the front end （ Convergence layer ） Switches are connected by network cables , Into optical signals , Use a single optical fiber to interconnect with the splitter at the user end . Realize the client device ONU The control of 、 management 、 ranging .

OPEN System consists of OLT port 、ONU port 、UNI(User Network Interface, User network interface ) Port composition .

Every OLT All ports correspond 64 A logical ONU port .

management OLT Way

The system mainly provides the following management approaches ：

· Access through HyperTerminal OLT Command line interface for （CLI）

· adopt telnet Management system

· adopt SNMP Management software management system

· adopt Web browser , Such as Internet Explorer Management system

1、 Login with HyperTerminal :
PC Connect to OLT/ONU Of Console mouth , So as to access the command line interface of the system through the HyperTerminal （CLI）.

OLT Access to electricity , After the system is successfully started , You can see the login prompt ;

Enter the correct user name , Press enter , Enter the corresponding password at the prompt . If it's the first time you log in OLT, You should use the default user name admin Sign in , Enter the login password admin, Operate as a system administrator . If you have assigned your user name and password , Then you can log in with your user name and password .

2、 Use Telnet Sign in
Connect the computer with OLT/ONU Port connection for ;
Run on the computer Telnet Program , One is DOS Run under telnet x.x.x.x, The other is to use SecureCRT( Enter after entering the interface OLT management IP Address , The port number is 1023);
to OLT Access to electricity , Type OLT Of IP Address , And OLT Establishing a connection , Enter the set login password according to the prompt .

4.1、OLT Common configuration

Symbol	describe
Vertical straight line I	The vertical line represents the juxtaposition relationship , This symbol is associated with [ ] or { } In combination with
brackets [ ]	The part enclosed in brackets means that you can choose to enter one of these commands , You can also leave it blank
{ x I y I … }	Indicates that only one... Is selected from multiple options
{ x I y I … }	Means from multiple options only Pick one
[ x I y I … ]	It means to select one or none from multiple options
{ x I y I … } *	Means from multiple options At least Pick one
[ x I y I … ]*	Means to select one from multiple options 、 Multiple or none
&<1-n>	A symbol & The previous parameters can be entered repeatedly 1～n Time
#	from “#” The line starting with the symbol is represented as a comment line

OLT The configuration is based on the domestic common H3C For example , Basic configuration port configuration ：

4.1.1、OLT To configure

1、 To configure OLT port

operation	command	explain
Get into OLT Port view	interface olt interface-number
OLT The link type of the port	port link-type hybrid	The default is Hybrid
Allow current OLT Port of VLAN	port hybrid vlan vlan-id-list{ tagged I untagged }	Allowed to pass VLAN Must have been created
Set up OLT Default port VLAN	port hybrid pvid vlan vlan-id	By default ,OLT Default port VLAN by VLAN1
Switch the current interface to GE Interface	port-type gigabitethernet	Switched GE The interface works in layer 2 mode by default

2、 To configure OLT Working mode
64-ONU Pattern ： Every OLT Ports support creation ONU The maximum number of interfaces is 64.

operation	command	explain
Configuration assignment slot Of OLT Working mode	olt-mode slot slot-number{ 64-onu I 128-onu }	Default is 64-ONU

3、 To configure ONU To OLT Maximum round trip time

• When ONU The equipment RTT Greater than OLT End configured RTT when , The ONU You will not be able to successfully register ;
• Set smaller RTT Value can reduce some optical power attenuation caused by long distance ONU Out of the EPON Beyond the system .
  RTT The unit is TQ（Time Quantum, Quantum of time ）.1TQ=16ns, It's equivalent to 1Gbps The rate of transmission 2 Time spent on byte data .

operation	command	explain
Get into OLT Port view	interface olt interface-number	Default is 64-ONU
To configure ONU To OLT Maximum round trip time	max-rtt value	By default , Maximum RTT The value is 15000TQ

4、OLT Display and maintenance